An access control system controls the lock. But controlling the lock only matters if the system also knows the state of the door. Is it open? Is it closed? Is someone coming through it right now? Without answers to those questions, the system is blind — it can unlock a door, but it can’t tell whether the door actually closed and re-secured afterward.
That’s where door position switches and request-to-exit (REX) sensors come in. They’re the inputs that tell the controller what’s happening at the door, in real time.
Door Position Switches (DPS)
A door position switch is a magnetic contact sensor. One half — the reed switch — mounts on the frame. The other half — the magnet — mounts on the door. When the door is closed, the magnet is close enough to the reed switch to hold it in one state. When the door opens, the magnet moves away and the switch changes state. The controller reads that change and knows: the door is open.
The DPS is the most basic monitoring input. Without it, the controller can unlock the door, but it has no way to know whether someone propped it open, whether it failed to close, or whether it was forced. The DPS turns a blind lock into a monitored opening.
On commercial aluminum storefront doors, the DPS is typically surface-mounted on the top rail of the frame, with the magnet on the top of the door. Concealed versions are available, where the switch and magnet are embedded inside the door and frame extrusion — but these require machining the aluminum and are harder to service.
Door Forced Open (DFO) Alarms
When the controller sees the DPS change from closed to open without an unlock command, that’s a door-forced-open event. The system was supposed to unlock the door first — someone was supposed to present a credential — but the DPS changed without that step. That means the door was forced. The controller logs the event and can trigger an alarm.
DFO alarms only work with a DPS. Without the switch, the controller has no way to distinguish between a door that was unlocked normally and one that was forced.
Door Propped Open (DPO) Alarms
When the DPS shows the door is open for longer than a set timeout — typically 30 to 60 seconds — the controller flags a door-propped-open event. Someone held the door, wedged it, or it failed to close. The system logs the event and can alert security or property management.
Request-to-Exit (REX) Sensors
A REX sensor tells the controller that someone is approaching the door from the inside. On an egress door — a door that people need to be able to exit freely — the REX sensor ensures the system unlocks (or the magnetic lock releases) when someone approaches, without requiring a credential.
There are two common types:
Passive infrared (PIR) REX detects body heat and motion. When someone walks toward the door from inside, the PIR sensor triggers and the controller releases the lock. PIR sensors are the most common type because they’re reliable, don’t require physical contact, and work well in most environments.
Mechanical REX — typically a push bar or a paddle — requires the person to physically push something to exit. These are used on doors where the REX needs to be intentional, not just motion-triggered. A mechanical REX is sometimes paired with a PIR as a redundant system.
Why REX Matters for Egress Compliance
On a door with a magnetic lock, the REX sensor is the primary means of free egress. If the maglock doesn’t release, people can’t get out — which is a life safety violation. The REX sensor has to be reliable, and on listed systems, it has to fail safe: if the sensor fails, the door unlocks.
Building codes — including the International Building Code and NFPA 101, Life Safety Code — require that egress doors allow free exit at all times, without special knowledge or effort. An access control system that requires a credential to exit is non-compliant. The REX sensor solves this: the person walks toward the door, the sensor detects them, and the lock releases.
How DPS and REX Work Together
The two sensors give the controller a complete picture of what’s happening at the door:
- Normal entry: Credential presented → controller unlocks → DPS changes to open (person enters) → DPS changes to closed (door swings shut) → controller re-locks.
- Normal exit: REX detects person approaching → controller releases lock → DPS changes to open → DPS changes to closed → controller re-locks.
- Forced entry: No credential presented → DPS changes to open → controller flags DFO alarm.
- Propped door: DPS stays open past timeout → controller flags DPO alarm.
Without both sensors, the system can’t distinguish between these scenarios. With both, every door event is logged, categorized, and actionable.
What Fails
DPS misalignment. If the door shifts on its hinges, the magnet on the door moves away from the reed switch on the frame — even when the door is closed. The controller reads the door as open when it’s actually closed, which triggers false DFO and DPO alarms. The fix is correcting the door alignment first, then re-aligning the DPS.
REX dead spots. PIR sensors have a coverage pattern — a cone of detection. If the sensor is mounted too high, too far from the door, or aimed incorrectly, there’s a dead zone where a person approaching the door isn’t detected. The door doesn’t unlock, and the person is trapped. The fix is repositioning the sensor and testing the coverage by walking the approach path.
Wiring failures. Both sensors run low-voltage wiring back to the controller. On aluminum storefront doors, the wiring routes through the frame extrusion and across the threshold — a path that’s vulnerable to chafing, water intrusion, and physical damage. A broken wire means the sensor goes dark, and the controller can’t read the door state.
What Pro Locksmith Does
Pro Locksmith LLC installs and services door position switches, REX sensors, and complete access control monitoring systems for commercial properties throughout Broward County and Miami-Dade, including Fort Lauderdale, Hollywood, Pembroke Pines, Davie, Pompano Beach, Coral Springs, and Miami. We design systems that maintain free egress at all times, with mechanical lock backup independent of the electronic system. Licensed and insured. Flat-rate pricing quoted up front. COI provided. Employees, not subcontractors.
If your access control system is generating false alarms or your REX sensors aren’t reliably detecting exit, call Pro Locksmith LLC at (954) 406-8266.
Sources
- NFPA 101, Life Safety Code (egress requirements)
- International Building Code, Chapter 10 (Means of Egress)
- ADA Standards for Accessible Design, Section 404